Single-crystal, 1D nanostructures are well known for their high mobility electronic transport properties. Oxide-nanowire field-effect transistors (FETs) offer both high optical transparency and large mechanical conformability which are essential for flexible and transparent display applications. Whereas the on-currents achieved with nanowire channel transistors are already sufficient to drive active matrix organic light emitting diode (AMOLED) displays; it is shown here that incorporation of electrochemical-gating (EG) to nanowire electronics reduces the operation voltage to 2 V. This opens up new possibilities of realizing flexible, portable, transparent displays that are powered by thin film batteries. A composite solid polymer electrolyte (CSPE) is used to obtain all-solid-state FETs with outstanding performance; the field-effect mobility, on/off current ratio, transconductance, and subthreshold slope of a typical ZnO single-nanowire transistor are 62 cm2/Vs, 107, 155 S/m and 115 mV/dec, respectively. Practical use of such electrochemically-gated field-effect transistor (EG FET) devices is supported by their long-term stability in air. Moreover, due to the good conductivity (approximate to 102 S/cm) of the CSPE, sufficiently high switching speed of such EG FETs is attainable; a cut-off frequency in excess of 100 kHz is measured for in-plane FETs with large gate-channel distance of >10 m. Consequently, operation speeds above MHz can be envisaged for top-gate transistor geometries with insulator thicknesses of a few hundreds of nanometers. The solid polymer electrolyte developed in this study has great potential in future device fabrication using all-solution processed and high throughput techniques.